Find which factor has the greatest effect on deciding the planform of the River Arrow in Herefordshire, by studying slope angle and discharge amongst other varying elements.
Kristina Gilbert
Geography A-level Coursework
River Study
Introduction
Study Area
Method
Pg 3
Pg 5
Pg 6
Introduction
The overall aim of this investigation is to find which factor has the greatest effect on deciding the planform of the River Arrow in Herefordshire, by studying slope angle and discharge amongst other varying elements.
Rivers are a primary feature of the world’s surface area. Hundreds of networks of river channels together drain almost 70 percent of the earth’s land surface and their characteristics differ from location to location and also at the same location over a time period, known as a river regime. In order to fully investigate the main question of this investigation, a number of subsidiary questions have been devised. Each of these in turn will help to provide answers in investigating the reasons for variation in planform.
- 1. How does the planform vary along the river?
- 2. Is the slope angle steeper on meandering bends than on straight
sections?
- 3. How do discharge and velocity compare on different planforms?
- 4. Does Channel roughness effect planform?
- 5. Does Landuse on the banks influence the planform shape?
Turbulent flow is the major flow type in most natural river channels. It is this which justifies their efficiency in both the eroding and transporting of materials and sediment. The velocity of a river is affected by three main things, channel roughness, channel shape and gradient. Channel shape can be described by the hydraulic radius of the water cross section, and is defined as the area of water per unit of channel water contact. The discharge of a river is dependant on the velocity of the river and the size of the channel at that point. The river’s velocity should increase as the discharge rises. The higher the velocity of a river, the more energy it has, and is therefore able to carry larger particles. A pattern should become apparent when comparing the velocity and discharge readings. The velocity of a river when at a gentler gradient should be greater than when it is at a steeper one. This is because the channel roughness and shape are more efficient in carrying water downstream and these two factors outweigh the effect that gradient will have on the river. If the river is surrounded by a vegetated area there may be variations in the discharge. Rainfall that reaches the ground surface does not flow immediately into the streams and rivers, but infiltrates into the soil and is transported to the rivers and streams later. Water can also be held in the vegetation above a river or stream if the precipitation is intercepted in the canopy layer. However, if the river or stream is in a built up, urbanised area, then the rates of run off are greater, and more water is likely to make it to the rivers at a quicker pace. River systems often provide us with a multivariate problem, as all variables affect eachother.